Learning Objective: Describe the key characteristics, functions, and clinical implications of deficiencies of water-soluble vitamins (B-complex and vitamin C).
Overview
Water-soluble vitamins include the B-complex vitamins and vitamin C. These vitamins act primarily as coenzymes or precursors to coenzymes in numerous metabolic reactions. They are easily washed out from the body (excreted in urine), except for vitamin B₁₂ (cobalamin) and vitamin B₉ (folate), which are stored in the liver.
Activity:
| Vitamin | Coenzyme / Function | Deficiency Findings |
|---|---|---|
| B₁ (Thiamine) | TPP – in dehydrogenase reactions | Beriberi, Wernicke-Korsakoff syndrome |
| B₂ (Riboflavin) | FAD, FMN – redox reactions | Cheilosis, corneal vascularization |
| B₃ (Niacin) | NAD⁺, NADP⁺ – redox reactions | Pellagra (3 Ds: diarrhea, dermatitis, dementia) |
| B₅ (Pantothenic acid) | CoA – fatty acid synthesis | Dermatitis, enteritis, and adrenal insufficiency |
| B₆ (Pyridoxine) | PLP – transamination, heme synthesis | Convulsions, peripheral neuropathy, and sideroblastic anemia |
| B₇ (Biotin) | Cofactor for carboxylation enzymes | Dermatitis, alopecia |
| B₉ (Folate) | THF – 1-carbon transfer | Megaloblastic anemia, no neurologic symptoms |
| B₁₂ (Cobalamin) | Cofactor for homocysteine → methionine | Megaloblastic anemia + neurologic symptoms |
| C (Ascorbic acid) | Antioxidant, collagen synthesis | Scurvy (bleeding gums, poor wound healing) |
Storage facts:
- B₁₂: stored in the liver for 3–4 years
- B₉: stored in liver for 3–4 months
General features of B-complex deficiency: Dermatitis, glossitis, and diarrhea.
